It is now needed that the development time and the fixing time can be shortened, as the performance of silver halide photographic materials, and for this purpose, silver chloride grains are noted. Silver chloride grains or grains high in silver chloride content (which mean grains having a silver chloride content of 50% or more, and which are hereinafter referred to as "high silver chloride grains") are materials well-known in the art, and are practically used in photographic materials for graphic arts printing and photographic materials for printing paper.
The high silver chloride grains are apt to be formed as grains having (100) faces on outer surfaces (hereinafter referred as to "(100) type grains") under conventional production conditions, and the grains practically used are cubic. In contrast, for silver iodobromide grains, grains mainly having (111) faces on outer surfaces (hereinafter referred to as "(111) type grains") can be easily produced, and the (111) type silver iodobromide grains are most frequently used in photographic materials for general photographing. In particular, the (111) type grains are easily formed in the tabular form, and it is possible to increase their specific area (the ratio of surface area to volume). Accordingly, they have advantages that they can be effectively subjected to spectral sensitization, and that they have high covering power after development. Also for the high silver chloride grains, therefore, it has been demanded to produce the (111) type grains.
Special means are required for the production of the (111) type high silver chloride grains. Wey discloses a method for producing high silver chloride tabular grains by use of ammonia in U.S. Pat. No. 4,399,215. The use of ammonia for the grains produced by this method further increase the solubility in the production of silver chloride grains having a high solubility, causing difficulty in producing practically useful small-sized grains. Further, the grains have the disadvantage of being liable to generate fog because they are produced at a high pH of 8 to 10. Maskasky discloses (111) type high silver chloride grains produced by use of a thiocyanate in U.S. Pat. No. 5,061,617. The thiocyanate increases the solubility of silver chloride similarly to ammonia.
Methods are known in which additives (crystal habit modifiers) are added in the grain formation in order to form the high silver chloride grains having (111) faces on outer surfaces, as shown below:
______________________________________ Patent No. Crystal Habit Modifiers Inventor ______________________________________ U.S. Pat. No. Azaindenes + Thioether Peptizers Maskasky 4,440,463 U.S. Pat. No. Thiazolidine-2,4-dione Takada 4,783,398 U.S. Pat. No. Aminopyrazolopyrimidine Maskasky 4,713,323 U.S. Pat. No. Bispyridinium Salts Ishiguro 4,983,508 U.S. Pat. No. Triaminopyrimidine Maskasky 5,185,239 U.S. Pat. No. 7-Azaindole Compounds Maskasky 5,178,997 U.S. Pat. No. Xanthine Maskasky 5,178,998 JP-A-64-70741 Dyes Nishikawa JP-A-3-212639 Aminothioethers Ishiguro JP-A-4-283742 Thiourea Derivatives Ishiguro JP-A-4-335632 Triazolium Salts Ishiguro Japanese Patent Monopyridinium Salts Ohzeki Application No. 7-146891 ______________________________________
The term "JP-A" as used herein means an "unexamined published Japanese patent application".
Among the above-described crystal habit modifiers, monopyridium salt is preferred as a photographic material because when it is used, efficiency in color sensitization is little reduced. This is disclosed in Japanese Patent Application No. 7-146891 and JP-A-2-32, and considered to be ascribable to weak adsorption of the crystal habit modifier to silver halide grains and accordingly, easiness in exchange adsorption by a sensitizing dye. This property of weak adsorption is in turn a defect that the grain is readily deformed during the production of an emulsion. Therefore, a technique for stabilizing the shape of a grain has been demanded.
In the present invention, a hexacyano complex is used. To improve the photographic performance by doping the complex to a grain has hitherto been attempted and an example thereof is disclosed in JP-B-48-35373 (the term "JP-B" as used herein means an "examined Japanese patent publication"). Also, European Patent application No. 0613044A (corresponding to Japanese Patent Application No. 5-35605) discloses a method for obtaining high sensitivity by doping an iron cyano complex to a silver chloride tabular grain produced using a bispyridinium salt. However, no conventional technique uses a hexacyano complex to a grain which is prepared using a crystal habit modifier having weak adsorption to a silver halide grain, such as a monopyridinium salt.